Is underlayment required under slate, tile, or thatch roofs?
Slate, tile, and thatch materials are not completely waterproof on their own and allow moisture to pass through joints and gaps. Underlayment serves as the actual primary waterproof barrier beneath these outer coverings, while the outer material functions mainly as UV protection.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1installing felt or underlayment anyway for extra security against wind-driven leaks
- 2relying purely on tight fitting slate without underlayment in certain regions
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“It was always my understanding during my entire career spanning over 40 years, that the slate is UV protection. The waterproofing was the underlayment. Same for tile and thatch roofs.”source ↗
BoonieRed · r/Roofing · 26 upvotes
“How wouldn't some water get in through those.”source ↗
Sasquatch_000 · r/Roofing · 9 upvotes
Where this came up
People with this problem also raised
- 2Do I need a vapor barrier over rigid foam in a basement?
- 4Do I need a waterproof membrane under tile on a concrete floor?
- 2Unexplained hole in attic roof decking
- 3How to know if a roof replacement quote is fair
- 12How to find where a roof leak is actually coming from
- 12How to tell if a new roof was installed correctly